This invention relates generally to devices used to provide safety for humans in proximity with moving equipment, and more specifically to motion and proximity sensors employed as part of a control system to orient equipment based on capacitance.
Safety is important when people are close to moving machines. One such example is locally controlled machines or robotic equipment where people are in close proximity to moving mechanical components. Another example is in the medical imaging equipment industry.
In known systems, conventional safety mechanisms such as mechanical switches and fluid-filled bladders connected to pressure switches are typically mounted directly to the moving mechanical components, or in proximity of the hazardous area. These conventional safety mechanisms require direct contact between the person or inanimate object and the safety mechanism to operate. For example, the fluid-filled bladder mounted to a moving mechanical component uses a pressure sensor or a pressure switch inside the bladder to detect increased pressure as the bladder makes contact with an object. The sensed pressure increase typically is an input to a control system which stops the moving mechanical component.
In other known systems, plates, levers, cables, and rings are connected to mechanical switches and mounted on the moving mechanical component. The switches are activated when the plate, lever, cables, or ring contacts the person or object, and the machine is stopped before any harm occurs.
Disadvantages of the above described systems include expense (fluidfilled bladders) and the fact that the sensing area is highly localized (mechanical switches). Such devices are typically ON or OFF and therefore provide no information to the control system regarding relative distance between the subject and the sensor. systems. The drawback to those systems is that an unobstructed line-of-sight between the detector and the subject is required. As applied to medical imaging equipment, required sterile covers and drapes preclude use of line-of-sight proximity detector systems. Depending on the implementation specifics, these sensors are also highly directional and impacted by object properties such as reflectivity and specularity, which further limits their applicability.
In the listed examples, safety cannot be enhanced, nor injury prevented simply by increasing the distances between man and machine because each example requires close proximity between man and machine. It would therefore be desirable to provide a system whereby proximity and relative distance to a person or an object can be sensed and the information regarding proximity and distance used to control movement and prevent contact with the person or object and thereby increase the safety of such a system.
In one aspect, the present invention relates to a method and system for detecting motion using a capacitance between a sensor and an object. Alternatively, the invention detects proximity of an object using the capacitance between a sensor and the object. In an exemplary embodiment, a capacitance based proximity sensor is used as a detector. The sensor includes sensing surfaces made of a thin film of electrically conductive material mounted on a non-conductive surface. The nonconductive surface can take any shape and form. The sensor senses the capacitance between a conductive surface and an object placed in its vicinity, and the sensor provides a capacitance value to a control system. The control system is programmed to use the capacitance data to control the movement of a machine or piece of equipment. In one embodiment, the piece of equipment is a medical imaging system.
In another embodiment, the sensing surface is a human body. A relative capacitance between the human body and surrounding objects is determined. The control system uses the capacitance information to determine a position of the body and proximity of objects near the body to control movement of a machine or piece of equipment.
Accordingly, because the sensor can take any size and shape, and does not require direct contact or line-of-sight with the object to determine if an object has moved, a machine or piece of equipment can be controlled before harm occurs to the object.